JPH0467754B2 - - Google Patents

Abstract

PCT No. PCT/GB83/00253 Sec. 371 Date Jun. 7, 1984 Sec. 102(e) Date Jun. 7, 1984 PCT Filed Oct. 11, 1983 PCT Pub. No. WO84/01674 PCT Pub. Date Apr. 26, 1984.The invention relates to a spark plug (1) comprising at least two insulated electrodes (5) and (6), an earthed electrode (7) and a chamber (4) so arranged with respect to one another that when a voltage is applied arcs are struck in series between electrodes (7) and (6) and (6) and (5) to provide a continuous plasma jet expelled from the chamber (4) at low energies (<100 mJ) and which can be used for combustion of a lean air/fuel mixture.

Description

Claim 1: A spark cavity with an internal region, an outlet from said internal region and three electrodes as a first electrode 5, a second electrode 6 and a ground electrode 7, all electrodes being insulated from each other, the first In the spark plug, a spark gap is formed between the first electrode 5 and the second electrode 6 inside the cavity 4, and a second spark gap is formed between the second electrode 6 and the ground electrode 7,
The two spark gaps are electrically arranged in series, the second spark gap being connected to the cavity 4.
A spark plug characterized in that it crosses the outlet of the spark plug.

2. the electrodes 6, 5 forming the first gap are arranged with the first electrode 5 disposed at the base of the inner region of the cavity 4, and on one side of the inner region;
a second electrode spaced apart from the first electrode 5;
an electrode 6, a part of the second electrode 6 being close to the outlet of the cavity 4, and an electrode forming the second gap connecting the second electrode 6 and the outlet of the cavity 4 from the second electrode 6; A spark plug as claimed in claim 1, characterized in that it comprises ground electrodes (7) arranged transversely at intervals.

3 The second electrode 6 and the ground electrode 7 are connected to the plug 1
The spark plug according to claim 1, wherein the spark plug is arranged in the same plane as the surface 3 of the spark plug.

4 The second electrode 6 and the ground electrode 7 are connected to the plug 1
3. The spark plug according to claim 1, wherein the spark plug extends outward from the surface 3 of the spark plug.

5 The second electrode 6 and the ground electrode 7 are connected to the plug 1
2. The spark plug according to claim 1, further comprising extensions 8, 9 which protrude outward from the surface 3 of the first insulated electrode 5 in a direction opposite to the first insulated electrode 5.

TECHNICAL FIELD OF THE INVENTION The present invention relates to a spark plug that can be used in internal combustion engines and other applications.

BACKGROUND ART In spark plugs that have already been proposed, combustion is initiated by plasma generated based on arc impact between two electrodes. Typically the spark energy is 30-40 mJ. These devices are incapable of igniting mixtures with air/fuel ratios significantly greater than stoichiometric.

Literature has shown that plasma jets are effective in igniting mixtures with high air/fuel ratios (e.g. SAE Technical Journal).
770355 and 800042). Other spark plugs for generating plasma jets at high air/fuel ratios require high energy (>1 J) to be dissipated in the arc.

DISCLOSURE OF THE INVENTION One object of the present invention is to seek to alleviate the above-mentioned disadvantages of conventional spark plugs.

The spark club according to the present invention includes at least two insulated electrodes and one grounded electrode arranged in series,
It is characterized in that the generated arc is generated in series between adjacent electrodes.

A spark plug embodying the present invention will be exemplarily described below with reference to the accompanying drawings.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of one typical conventional spark plug, FIG. 2 is a schematic vertical cross-sectional view of another conventional spark plug, and FIG. 3 is a schematic vertical cross-sectional view of a spark plug according to the present invention. 4 is a schematic vertical sectional view showing a second embodiment of the spark plug according to the present invention, and FIGS. 5 to 8 are schematic vertical sectional views showing various electrode shapes of the spark plug according to the present invention, respectively. FIG. 9 is a schematic longitudinal sectional view showing yet another embodiment of a spark plug according to the invention, and FIG. 10 is a schematic diagram showing the arrangement of a drive unit for the spark plug according to the invention.

Referring to the drawings, FIG. 1 shows a spark plug in which combustion is initiated by plasma generated by arc impact between electrodes A and B. Typically this spark energy is 30~
It is 40mJ. Such plugs cannot ignite mixtures with air/fuel ratios significantly greater than stoichiometric. FIG. 2 is a sectional view showing relevant parts of another conventional spark plug. This plug is high sky/
A plasma jet can be generated to ignite the combustion mixture at a fuel ratio. The arc is energized between the end electrodes A and the central insulated electrode B in the cavity C in the ceramic body D. Sufficient energy (>1 J) is dissipated in the arc and a high level of ionization occurs within cavity C. The energy consumed heats the gas and causes it to expand rapidly.
As a result, ionized gas is ejected from the cavity C as a plasma jet E.

Spark plugs embodying the present invention are Nos. 3 to 9.
In the figures, the same reference numerals refer to the same parts. Referring to FIG. 3, a spark plug 1 of the present invention basically constitutes a twin gap type spark plug for generating plasma jet E.
It is shown. The spark-forming part of the spark plug 1 comprises an insulator consisting of a ceramic body 2 terminating in a surface 3. This insulation surrounds a cavity 4 containing a central insulated electrode 5. The plug is further equipped with an insulated electrode 6 and a ground electrode 7. These electrodes are separated from each other and form rows of cooperative electrode pairs 7-6 and 6-5.

The spark plug 1 of the present invention operates as follows.

The arc is energized simultaneously between the electrodes 7, 6 and between the electrodes 6, 5, forming an arc row between the electrodes 7, 6, 5. The heat generated by the arc between the electrodes 6 and 5 causes the gas within the cavity 4 to expand and eject from the cavity 4. When the gas thus expanded is discharged from the cavity 4, it is ionized by passing through the arc between the electrodes 7, 6. As a result, a plasma jet is generated as shown at E in the diagram.

Such plasma jet generation systems are extremely efficient and require less than 100 mJ, e.g.
It operates satisfactorily with spark energy within the range of 50 to 100 mJ.

The device operation generates a self-stabilizing function due to the negative feedback effect based on the inherent design. The arcs between electrodes 7 and 6 and between electrodes 6 and 5 are in series. The tendency of the expanded gas to extinguish the arc by passing through it results in a reduction in the arc current. This reduction in arc current reduces the current forming the arcs 6,5. As a result, heat dissipation within the cavity 4 is reduced. Therefore, the gas expansion slows down, and eventually the momentum to extinguish the arcs 7, 6 decreases. In this way, two spark gaps arranged in series are effectively used. That is, one spark gap heats and expands the gas inside the cavity. The other gap straddles the entrance and exit of the cavity and ionizes the expanding gas that is about to be discharged from the cavity. In this case, a plasma thermal energy of less than 100 mJ can be generated.

Referring to Figure 4, a longitudinal cross-section of a portion of a spark plug 1 according to the invention is shown. The spark plug is capable of generating a plasma jet for igniting a high air/fuel ratio combustion mixture. The spark-forming part of the spark plug 1 has an insulator consisting of a ceramic body 2 terminating in a surface 3. This insulator has a cavity 4 containing a central insulated electrode 5.
is surrounding. The ceramic body is further provided with an insulated electrode 6 and a ground electrode 7.

As is clear from the figure, the electrodes 6 and 7 each protrude upward from the surface of the ceramic body 2. In the illustrated embodiment, the protrusions 8 and 9 of the electrodes 6 and 7 extend upward while opening from each other.

When the spark plug described above is used, arcs occur simultaneously between electrodes 7, 6 and 6, 5, forming an arc train across these electrodes. The expanded gas discharged from the cavity 4 forms a sheet-like discharge as shown at 10. This sheet-like discharge effect is not produced solely by energizing the arc between the electrodes 7, 6, which is intended only for the usual narrow spark discharge. Spark plug 1 according to the invention
Therefore, the heated gas that expands within the cavity 4 and ejects from it is ionized, and the arrow "E"
It forms a sheet discharge that generates a plasma jet as shown in . Jet E provides combustion reliability for unfavorable air/fuel mixtures.

The protrusions 8 and 9 of the electrodes providing a sheet discharge effectively extend the gap of the spark plug;
Moreover, this means that the voltage needed to achieve combustion is not increased.

Furthermore, the spark for gas ionization is self-stabilizing. That is, the tendency of the spark between the electrodes 6, 7 to be blown out by the expanding gas exiting the cavity 4 reduces the arc current and therefore reduces the heat dissipation within the cavity 4, thereby slowing the gas expansion. This reduces the tendency of the spark between the electrodes 6, 7 to extinguish, thus maintaining the sheet discharge 10 and providing comprehensive ionization of the gas. The overall effect is that the plasma jet E is maintained.

Plasma jet E can generate less than 100 mJ of energy in such a plug according to the invention.

As a variant of the spark plug described and illustrated above, it is also possible, for example, for the projections 8 and 9 to be convergent or substantially parallel.

5-8, various electrode shapes of spark plugs according to the present invention are shown. Fifth
In the figure, electrodes 6 and 7 are of the flat type, flush with surface 3, but in FIG. 6 electrodes 6 and 7 are shown as protrusions from surface 3. FIG. 7 shows an electrode in which the surface 3 itself is sloped to form a substantial frustoconical shape, with electrodes 6 and 7
A slanted electrode protruding from the surface 3 as shown in the figure is formed.

The jet motion used in this embodiment represents a fresh feed to the active area in close proximity to the plug, thereby activating the mixture and improving burnup.

Also in FIG. 8, electrodes 6 and 7 have protrusions 8 and 9, respectively. These electrodes are placed on the surface of the insulator with maximum exposure for fueling the arc.

5 to 8 show a metal body 11 with a threaded portion for screwing the plug 1 into an internal combustion engine. In these plugs, the central rod electrode 5 is inserted with the surface exposed into the cavity 4 into a suitable plastic material 12, such as polytetrafluoroethylene (PTFE).

FIG. 9 shows another embodiment of the spark plug electrode 6 including two parts 6A and 6B, which are electrically connected as shown. As shown, between electrodes 7-6A and 6B-5
Arc rows are generated between the protrusions 8 and 9, respectively.
A sheet discharge portion is formed in between.

In Figures 5-9 the exit from the cavity 4 is narrower than the cavity itself. In FIG. 9, the width of the outlet is 1 mm, the volume of the cavity 4 is 28 mm ³ and the length of the protrusion is 3 mm. By length of the protrusion is meant the vertical distance from the free end of the protrusion to the surface 3.

In the embodiment shown in FIGS. 4, 8 and 9,
For example, the protrusions 8 and 9 are formed by wires or tubes carried on the electrodes 6, 7, or by desired extensions formed integrally with the electrodes. These protrusions provide continuous combustion of the undesirable mixture by modifying the shape of the arc/plasma jet. The stable sheet discharge formed in each embodiment can be generated at low energies and is useful for igniting combustion mixtures with unfavorable air/fuel ratios in internal combustion engines.

FIG. 10 schematically shows a drive unit for driving a spark plug 1 embodying the invention.

Plug 1 is connected to battery 12 (+350V power supply),
It is connected in a circuit including an electronic switch 13, a capacitor 14 and an ignition coil 15.

The capacitor has a capacitance of 1 μF.

Therefore, the energy stored in this is CV ² /2=60mJ.

By using this circuit and closing the switch for 0.5 msec, the spark current, which has a peak value of approximately 75 mA, will drop exponentially to 20 mA after 0.5 msec has elapsed.
The peak value is mA, and the circuit exhibits damped oscillation (ringing) at approximately 4KHz.

The volume of the cavity 4 can be varied by adjusting the position of the electrode 5 with respect to the body 2.

The distance between the opposing surfaces of electrodes 6 and 7 is the width/diameter ratio.
0.508 mm, which is also equal to the lateral extent of the cavity. the bottom (as shown) of the electrode 6;
The distance from the top of the electrode 5 (as shown) may be 0.381 mm.

A spark plug embodying the present invention can be applied not only to internal combustion engines but also to various devices.

For example: 1 Other types of engines in which plugs can be used: (a) gas turbines (b) gas engines (c) spark-ignited diesels (d) other types of engines in which combustion is initiated by a spark 2. Can be used as a device igniter.

(a) Boilers (b) Heaters (c) Process equipment (d) Gas jets (e) Blow lamps (f) Torches 3 The plug of the present invention can be used in fields suitable for using pulsed ion sources.

(a) Cleaning effect by ion bombardment (b) Surface treatment (c) Surface-induced chemical change (d) Trigger of electrical discharge (e) Display (f) Induced chemical reaction In all examples, two arcs in series were used. The use allows a more efficient use of energy, most of which is dissipated in the arc and only a small amount in the (external) drive circuit.